The aims of this research project are to fully characterize the sarcomere striation pattern positions and sarcomere length distributions throughout the volumes of Ca++ tolerant isolated cardiac cells to evaluate (a) the preparation as an interpretable model of myocardial mechanics and (b) the asymmetries and precision of the light diffraction technique. Ca++ tolerant isolated cells, or myocytes, will be prepared by enzymatic digestion of rat myocardium. Optically discrete cell volumes will be sequentially imaged along lateral and focal planes of selected isolated cells with a high-resolution computer interfaced imaging system. The A-I band striation pattern will be imaged through a high-resolution Nomarksi contrast enhanced optical microscope onto an external solid state detector which is interfaced to a digital computer. Striation pattern images are digitally processed to determine individual striation positions throughout the small (120 x 20 Mum) isolated cells. Sarcomere length and distribution data will be obtained from isolated cardiac cells at rest or during paced electrical contractions in either a free state or when constrained by vacuum suction microelectrode pipettes. The regional sarcomere length distributions will be evaluated to determine the magnitude of internal cellular elastic strains that influence sarcomere uniformity and contractile kinetics. These data will also be the source for numerical calculations of light diffraction patterns which provide a direct interpretable correlation between the actual muscle structure and its pattern.